Internal combustion reciprocating engine (ICRE) design has been in transformation for some time due to the demands for increased engine efficiency and lower emissions. Non-conventional fuel blends, and ultimately alternative fuels, are anticipated to come into increasing use. In response, engine designers have been re-examining engine attributes, including the actuation of the gas exchange valve (GEV), i.e. the intake and exhaust valve. In its present forms the ubiquitous poppet valve, with cam shaft actuation and coiled metal spring valve closure, are generally seen as inadequate for future engine requirements. Over the last several years there has been considerable effort expended on valve actuation (VA) as well as variable valve actuation (VVA) and a great number of patents have been issued in this area. Of these, the electro-hydraulic valve actuator (EHVA) is the focus the present invention. This class includes both the basic function of valve actuation (valve opening and valve closure) and variable valve actuation (varied valve timing, open/close duration and amount of valve lift).
Notable among the EHVA designs are the valve actuators disclosed by Sturman or its assignees—see: U.S. Pat. Nos. 7,025,326, 6,557,506, 6,360,728, 6,308,690, 6,148,778, 5,829,396, 5,713,316, 5,640,987, and 5,638,781. The foregoing patents are based primarily on the original Sturman design of a latching solenoid, disclosed in U.S. Pat. Nos. 3,743,898 and 3,683,239 (first applied to Diesel fuel injectors). This latching solenoid device is employed in the Sturman EHVA to move a linear hydraulic spool valve, which then provides hydraulic pressure and flow to an actuating hydraulic cylinder. In this design, as disclosed in U.S. Pat. No. 5,638,781, the valve operation is either open or closed. Quoting from its abstract: “—Energizing one solenoid moves the spool and valve into an open position. The valve spool is maintained in the open position by the residual magnetism of the valve housing and spool even when power is no longer provided to the solenoid. Energizing the other solenoid moves the spool and valve to a closed position. The solenoids are digitally latched by short pulses provide by a microcontroller. The valve is therefore opened by providing a digital pulse of a short duration to one of the solenoids and closed by a digital pulse that is provided to the other solenoid.—”. That is, the valve is either fully open or fully closed. Sturman discloses, in U.S. Pat. No. 5,638,781, an EHVA with integrated double acting hydraulic cylinder (which eliminates the need for a GEV return spring) and digital solenoid spool valve. To add an additional degree of valve control, Sturman further discloses, in U.S. Pat. No. 7,025,326, a design and method which adds a proportional hydraulic control valve function, with the objective of reducing the power consumption of the valve actuation system. However, this addition has a higher degree of complexity and an associated cost increase compared to the “digital” version. Sturman valve actuators have demonstrated satisfactory on-engine performance and the introduction of a Sturman EHVA into a production truck engine is imminent. Nonetheless, the latching solenoid principle appears to be limited to relatively modest sized EHVA—due the required properties of the magnetic circuit.
Schechter discloses in U.S. Pat. No. 5,456,222 (assigned to Ford Motor company) a reversing electric motor with a threaded shaft coupled to a threaded hydraulic valve spool—to convert the motor rotary motion to linear motion for the reciprocation of the spool valve. The hydraulic spool valve produces reversible hydraulic fluid flow to an integral double acting actuating cylinder (no valve spring) for a GEV. The requirement for reversing the motor is a disadvantage as it degrades valve response compared to a motor with continuous rotation.
Eaton discloses in U.S. Pat. No. 5,682,846 an EHVA with solenoid spool valve and an integral double acting hydraulic cylinder actuator with dual pistons of two different diameters, providing greater actuation force onto the GEV—than similar prior devices.
Buehrle discloses in U.S. Pat. No. 6,024,060 a unique rotationally oscillating electric motor directly driving a hydraulic control valve supplying hydraulic fluid to a separate single acting hydraulic cylinder actuating the GEV.
Cummins discloses in U.S. Pat. No. 6,067,946 a device utilizing one or more hydraulic pressure sources applied through solenoid valves to a separate single acting hydraulic cylinder actuator for a GEV with varying return spring configurations.
Each of these inventors devices, Sturman, Schechter (Ford), Eaton, Cummins, and Buehrle, have limitations such as speed, operating range, capacity, cost, power consumption, etc.—which other designers are endeavoring to overcome. For example, see “Development of a Piezoelectric Controlled Hydraulic Actuator for a Camless Engine” Thesis of J. S. Brader, University of South Carolina, 2001—that demonstrated a successful proof of concept piezoelectric stack, hydraulic spool valve and actuator device. Also see: “Dynamic simulation of an electro-hydraulic open center gas-exchange valve actuator system for camless internal combustion engines.” Thesis, J. M. Donaldson, P. E., Milwaukee School of Engineering, 2003—in which modeling of an open-center hydraulic series valve system demonstrated the feasibility of the concept.
The present invention is an electro-hydraulic valve actuator (EHVA) intended to provide a more optimal balance of the wide range of design aspects required of EHVA, including: capacity, speed, lift, profile, cost, etc.—thereby satisfying the requirements of a broader range of ICRE and providing an improvement over the existing EHVA art. It utilizes a rotary “plug” valve which has the potential for very high speed, (>10,000 rpm or 20,000 rpm engine speed) thus allowing the present invention to meet the speed requirement of any known ICRE. As a single acting actuator, the present invention's speed is however, ultimately limited by the valve spring. The present invention is scalable over the entire range of ICRE sizes from micro engines to the largest Diesel contemplated. In addition, the present invention may be implemented with a varying range of components to meet cost objectives—for example a switched reluctance motor versus a permanent magnet motor. The recent commercial availability of a wide range of brushless electric motors and dedicated integrated driver circuits has made the present invention viable. Nonetheless, it is unlikely there will be just one solution to improved ICRE valve actuation as the range of engine requirements is highly diverse.